GO LANGUAGE AND MONGO DB HACK #2

Hack #2  : GO LANGUAGE AND MONGO DB

URL Shortener

I stated writing my new blog "weekforhack".

URL SHORTENER HACK #1 : URL shortener client.

C++ Using Namespace

Here is sample code to show the use namespace in C++.

#include<iostream>
 namespace ns1

{
 void print(){
 std::cout<<"namespace ns1"<<std::endl;
 }
}

 namespace ns2
 {
   void print(){
     std::cout<<"namespace ns2"<<std::endl;
   }
 }


 int main(){
   using namespace ns2;
   ns1::print();
   ns2::print();
   print();

   return 0;
 }

output :

namespace ns1
namespace ns2
namespace ns2

Similarly, using namespace std is defined as :

// iostream header file
namespace std
{
   ostream cout;
   istream  cin;
   // 
};

Json File parsing in IOS

NOTE : need some changes
json file (test.json)

{

"commands":[

                {"command" : "Home", "method":"homemethod",  "image" : "homemg" },

                {"command" : "Exit", "method":"exitmethod",  "image" : "exitimg" },

    ]

}

step 1 :

   reading file test.json

   NSString* path = [[NSBundle mainBundle] pathForResource:@"test"

                                                     ofType:@"json"];

    NSString* content = [NSString stringWithContentsOfFile:path

                                                  encoding:NSUTF8StringEncoding

                                                     error:NULL];

step 2 :

 nsstring to nsdata

NSData* data = [content dataUsingEncoding:NSUTF8StringEncoding];

step 3 :

dict from nsdata

NSMutableDictionary *dict=[NSJSONSerialization JSONObjectWithData:data

                                                       options:NSJSONReadingMutableContainers

                                                         error:&error];

step 4 :

  test 

for(NSDictionary *d in array){

        NSLog(@"---------------------------");

        NSLog(@" command -- %@",[d objectForKey:@"command"]);

        NSLog(@" method -- %@",[d objectForKey:@"method"]);

        NSLog(@" image -- %@",[d objectForKey:@"image"]);

        NSLog(@"---------------------------");        

    }

    

}

A good tutorial on GIT

I wanted to share a good link to understand working of git.
The following link explained the git in different way

http://www.sbf5.com/~cduan/technical/git/

I found a very good project to understand branching on github :
https://github.com/pcottle/learnGitBranching

Happy Coding.. :) B-)

Closure in Python

Yesterday i tried closure , One can easily use the function as variable 

You can see my session here and use of closure :

...:) B-)

Reference :

http://www.shutupandship.com/2012/01/python-closures-explained.html

Screen : An awesome terminal tool

Today, i get to know about a awesome tool : Screen. Sometimes we need to switch among the terminal to see them. Screen simplified the whole thing.
Now one can see the more than one terminal on single terminal view.

Here , you can see my terminal :

I divided my terminal into horizontal and vertical subterminals.

Following are the steps to use screen :

1. install screen :
       sudo apt-get install screen

2. on terminal write screen and press enter. follow the instruction.

3. split screen
       Horizontal :
                 press ctrl+a then S (upper case)
        Vertical :
                 press ctrl+a then |
4. start screen
               press ctrl+a then c

enjoy your terminal ...


:) B-)

Reference :
http://www.rackaid.com/resources/linux-screen-tutorial-and-how-to/
http://unix.stackexchange.com/questions/7453/how-to-split-the-terminal-into-more-than-one-view

Communicating with two language

Previously we implemented the python server. Now it's time to bring up our client part.
Android Client will send downloading url to Python server and Python Server will download the passed URL.

You can see the code repository (Python Server) :
 https://github.com/subh007/Python/blob/master/server_PC.py

You can see the code repository (Android Client) :
 https://github.com/subh007/Android_Client/tree/master/AndroClient

screen shot of client:

Android Client

Python Server

:) B-)

String handling in Python

Sometimes we get a url and we need to retrieve the filename from the url ( like http://some_url/filename.mp3).

This can be done easily in python.

>>> string = 'http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjectiveC/ObjC.pdf'
 
>>> string.split('/')
['http:', '', 'developer.apple.com', 'library', 'mac', 'documentation', 'Cocoa', 'Conceptual', 'ObjectiveC', 'ObjC.pdf']
 
>>> print string.split('/')[-1]
ObjC.pdf


:) B-)
 

Threading in Python

My previous post were related to server and client. I need to enhance my server
so that it can handle multiple clients.

To handle such requirement i thought to redesign my server. Each client request
to server and server will start download in separate thread for requested url.
This will enhance my server design and now my server can handle multiple client
simultaneously.

So here is some threading concepts in python:

There are two ways to specify the activity: by passing a callable object to the constructor, or by overriding the run() method in a subclass.

A simple example:

 import threading
 import datetime
        
 class ThreadClass(threading.Thread):
          def run(self):
            now = datetime.datetime.now()
            print "%s says Hello World at time: %s" % 
            (self.getName(), now)
        
 for i in range(2):
          t = ThreadClass()
          t.start()

Another more simplistic example :

import time
from threading import Thread

def myfunc(i):
    print "sleeping 5 sec from thread %d" % i
    time.sleep(5)
    print "finished sleeping from thread %d" % i

for i in range(10):
    t = Thread(target=myfunc, args=(i,))
    t.start()

-- :) B-)
       
Reference :
http://docs.python.org/library/threading.html
http://www.ibm.com/developerworks/aix/library/au-threadingpython/
http://www.saltycrane.com/blog/2008/09/simplistic-python-thread-example/

Source code:
https://github.com/subh007/Python/blob/master/multithread1.py
https://github.com/subh007/Python/blob/master/multithread.py

Server extended to download file.

In previous post i created a server-client pair using the python.
It is enhanced in such a way that client will pass a download link
to server and server will download the link.

import sys
import socket
sys.path.append('/home/subhash/subh/python/requests')
import requests
s=socket.socket()
hostname=socket.gethostname()
port=9595
s.bind((hostname,port))
s.listen(5)
while True:
    print 'server started'
    conn,addr=s.accept()
    data=conn.recv(1024)
    print(data)
    r=requests.get(data)
    with open('downloded.pdf',"wb") as code:
     code.write(r.content);
     print 'page downloaded'
    conn.close()
s.close()


you can see the code in git. :) B-)

How to kill the process at port XXXX

Sometime we require to kill the process at port.

For example.

s=socket.socket()
hostname=socket.gethostname()
port=9494
bind((hostname,port))

...
..
(pressed ctrl+d)

this will cause the process to still run on port 9494. So whenever we try to
bind the same port to another proce then it will give error:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/usr/lib/python2.7/socket.py", line 224, in meth
    return getattr(self._sock,name)(*args)
error: [Errno 98] Address already in use

So, we need to kill the process at that port and it is done by:

$kill -9 `fuser -n tcp 9494`

:) B-)

Download files using request

This is simple example to use request for downloading the files.

import urllib

import sys

#adding the requests http://docs.python-requests.org/en/latest/index.html

import requests

print sys.argv[1]

# url to download

r=requests.get(sys.argv[1])

with open(sys.argv[2],"wb") as code:

#argv[2] is target file name

 code.write(r.content)

 

here, argv[1] is the link for the download file ( ex.- https://google.com) 

and argv[2] is the target file (ex. google.html).

run it by

#python script.py http://google.com google.html

happy coading :) B-)

Reference:

download code from git

http://docs.python-requests.org/en/latest/

Simple Server - Client program in python

I got a good example for server client in python.

Server :

#!/usr/bin/python           # This is server.py file

 import socket               # Import socket module

s = socket.socket()         # Create a socket object

host = socket.gethostname() # Get local machine name

port = 12345                # Reserve a port for your service.

 

print 'Server started!'

print 'Waiting for clients...'

 

s.bind((host, port))        # Bind to the port

s.listen(5)                 # Now wait for client connection.

c, addr = s.accept()     # Establish connection with client.

print 'Got connection from', addr

while True:

   msg = c.recv(1024)

   print addr, ' >> ', msg

   msg = raw_input('SERVER >> ')

   c.send(msg);

   #c.close()                # Close the connection

Client :

#!/usr/bin/python           # This is client.py file

 

import socket               # Import socket module

s = socket.socket()         # Create a socket object

host = socket.gethostname() # Get local machine name

port = 12345                # Reserve a port for your service.

 

print 'Connecting to ', host, port

s.connect((host, port))

 

while True:

    msg = raw_input('CLIENT >> ')

    s.send(msg)

    msg = s.recv(1024)

    print 'SERVER >> ', msg

#s.close                     # Close the socket when done

Reference :
http://www.dscripts.net/2010/06/18/how-to-create-a-client-server-socket-connection-in-python/

 

installing libcap

I faced lot of problem in installing libcap (library for sniffing packet). You can easily install it in ubuntu by installing the package libpcap0.8-dev.

#sudo apt-get install libpcap0.8-dev

and during compilation of any program using pcap.h
 compile it

#gcc prog.c -lpcap -o prog

enjoy coding.. :) B-)